The present invention relates generally to systems for protecting aircrew members from the adverse physiological effects of brain oxygen-depleting environmental stressors, and more particularly to a warning system for informing an aircrew member undergoing high acceleration of the time remaining before fatigue sets in and the aircrew member will no longer be able to maintain straining maneuvers intended to fight the effects of high acceleration.
Many types of environmental stressors deplete the oxygen available to an aircrew member. For example, while flying simulated or actual combat maneuvers, a fighter pilot's body undergoes very high accelerations from the rapid changes in speed and direction. These accelerations are generally expressed in units of g, the acceleration of a mass at the surface of the Earth due to gravity. The accelerations of greatest concern to a pilot are those that occur along the vertical Z-axis of the cockpit when the pilot pulls back hard on the aircraft control stick to accomplish a rapid climb or a fast banked turn. The pilot's oxygen-carrying blood is forced away from its regular path between the heart-lungs and the brain and pools toward the blood vessels of the lower extremities. At sufficiently high G's, or after a sufficient length of time at high G's, the pilot's field of vision narrows as blood flow to the retinas is reduced, and the pilot will finally lose consciousness due to insufficient blood flow to the brain.
High altitude is another environmental stressor that depletes the oxygen available to an aircrew member. Whether the decreased oxygen level is from hypoxic hypoxia (decreased blood oxygen levels from decreased available oxygen in the atmosphere) or from stagnant hypoxia (blood pooling in the lungs and other body regions during exposure to hypergravity), the physiological end result is the same.
Aircrew members fight the adverse effects of high G's by straining maneuvers, isometrically tensing the muscles of their torso and extremities to squeeze shut the blood vessels and force blood flow to continue in the upper part of the body. These straining maneuvers typically can be maintained for only a limited period of time before fatigue sets in and the aircrew member can no longer resist the effects of high G's. Without warning of the onset of fatigue, the aircrew member may experience G-induced loss of consciousness (GLOC) before being able to take steps to reduce the environmental stressor, such as by moving the control stick to unload the aircraft.
Aircrew members fight the adverse effects of other brain oxygen-depleting environmental stressors by a variety of other methods, such as by different breathing procedures or by breathing supplemental oxygen during high altitude flight. A pilot may also descend the aircraft to a flight level below 10,000 ft.
The prior art includes various non-invasive loss of consciousness monitoring devices for aircrew members. Two useful examples of such devices, both of which have a co-inventor of this invention as an inventor or co-inventor, are "Ear Canal Pulse/Oxygen Saturation Measuring Device," U.S. Pat. No. 5,213,099; and, "Intrusion-Free Physiological Condition Monitoring of Flyers," Statutory Invention Registration (SIR) No. H1039, both of which are incorporated by reference into this description. Those two monitoring devices non-invasively monitor blood oxygen saturation levels so that when monitored blood oxygen saturation levels fall to a level indicating imminent unconsciousness, an alarm can be sounded or control of the aircraft removed from the pilot and the aircraft unloaded to reduce G-loading.
The prior art has not, however, explored the possibility of displaying blood oxygen saturation levels to the pilot or other aircrew member so that they can respond to that information before GLOC occurs. Part of the reason for this is that, except for actual GLOC, or other caused unconsciousness, the practical physiological meaning of various levels of blood oxygen saturation has not been well understood. Without such information, the ability to monitor in realtime blood oxygen saturation levels has been of limited utility.
Thus it is seen that there is a need for discovery of the practical physiological effects of different blood oxygen saturation levels.
It is also seen that there is a need for apparatus and methods for utilizing such discovered information that will help aircrew members avoid the harmful effects of brain oxygen-depleting environmental stressors.
It is, therefore, a principal object of the present invention to provide an apparatus and method for measuring blood oxygen saturation levels of an aircrew member and, using that information, displaying to the aircrew member useful information concerning the adverse effects of high G.sub.z acceleration and brain oxygen depletion.
It is a feature of the present invention that it incorporates a discovery that relates percentage blood oxygen saturation to the time remaining before an aircrew member will no longer be able to maintain performance.
It is another feature of the present invention that it displays to an aircrew member the time remaining before that aircrew member will no longer be able to maintain performance.
It is an advantage of the present invention that it enables aircrew members to make knowledgeable decisions during combat or other high intensity activities about, for example, the time of initiation and the duration of combat maneuvers.
It is another advantage of the present invention that because aircrew members will have a realtime display of the time remaining before performance-ending fatigue sets in, they can, and will, develop techniques to extend that time and increase overall performance.
It is an outstanding advantage of the present invention that it is an incentive to better performance. Because a pilot can now be shown the time remaining during which he or she can expect to continue a high level of performance, despite the presence of environmental stressors, he or she will try harder to reach and maintain that level of performance for at least the period of time displayed and, more likely in view of the competitive nature of pilots, even to exceed it.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.